Drilling mud



Patented Dec. 19, 1944 DRILLING MUD Donald 0. Bond, Northbrook, Ill.,assignor to The Pure Oil Company, Chicago, 111., a corporation of OhioNo Drawing. Application June 9, 1943,

Serial No. 490,191

18 Claims. (Cl. 252-85) ,This invention relates to drilling wells and isprimarily concerned with the production of an improved drilling mud andcomposition for preparation thereof for use in the drilling of wells,especially oil and gas wells, and with the method of drilling wellswherein such muds are used. Thi application is a continuation-in-part ofmy co-pending application Serial No. 303,024 filed November 6, 1939,entitled Improved drillingmud.

Drilling operations are usually conducted in the presence of acirculation of mud, that is, water containing mineral matter such asclay in a finely divided or defiocculated state. Such drilling muds areused in almost all rotary drilling operations for deep wells for oil andgas and simultaneously serve several functions. The

Y mud is used primarily to carry the cuttings from the hole and tolubricate the drill bit, and in addition provides a lining or sheath onthe walls of the drill hole to prevent either flow of water or gas fromthe sub-surface formation into the drill hole or to prevent loss ofdrilling fiuid from the hole into the formations through which the holeis drilled. These muds are frequently made from material native' to theformation in which the well is drilled, although it is often necessaryto add additional material to the mud which will increase the specificgravity in order to increase the weight of the column of mud in the welland thereby offset the effect of high gas pressure.

oxide and barytes are commonly used. Every natural clay containsparticles of many orders of magnitude, some being coarse enough tosettle out of a water suspension quickly and others being fine enough tostay suspended for indefinite periods. In a clay that is considered goodfor drilling purposes the fine material is predominant and is in anindefinitely fine state of subdivision, the finest being so small thatmuch or most of it can be said to be in the form of a colloidalsuspension or dispersion when the clay has been mixed with water. Thesuspended particles obey the general rules of colloidal dispersions, thedegree of dispersion being increased by some ions and chemicals andbeing decreased by others. An

For this purpose weighting materials such as iron increase in the degreeof dispersion is termed deflocculation and a decrease in the state ofdispersion is termed flocculation. Flocculated clay may be-in an equallyfinely divided state to that of deflocculated clay but the flocculatedmaterial will come together in -flocculent, loose clumps or aggregateswhich settle readily from the medium in which it is dispersed, which inthe case of drilling muds, is generally water. The stability ofcolloidal dispersions is also directly related to the charges on thedispersed particles. In general it may be said that strongly chargednegative or positive particles form stable dispersions, whereas weaklycharged or neutral particles tend to flocculate and settle out of thedisperse medium.

When drilling in some formations such as, for example, certain shaleformations, considerable difiiculty has been experienced due to theproperty of these shale formations of swelling and sloughing whencontacted with water or ordinary drilling mud. This property of someformations to hydrate or absorb water and swell sometimes occurs to suchan extent that the holes cave and fill to such a degree that in the endthe drilling has to be. abandoned. Formations which have this propertyof absorbing water and swelling are, in the well drilling art, generallytermed heaving-shale formations and it is with these types of formationsthat this invention is particularly concerned.

It is an object of this invention to provide an improved compositionuseful in the preparation of drilling mud.

It is another object of this invention to provide an'improved drillingmud which will prevent the heaving of heaving-shale formations.

It is a still further object of this invention to provide a drilling mudin which the colloidal mineral content is dispersed as positivelycharged particles.

A further object of this invention is to provide an'improved methodfordrilling in heavin -shale formations. 4

Various other objects and advantages will appear as the description ofthe invention proceeds.

Colloidally dispersed clay, obeying the general rules of colloidaldispersions, carries an electrical charge. Practically all naturallyoccurring finely divided clays such as kaolin and bentonite carrynegative charges on the dispersed particles when dispersed in an aqueousmedium. It is known that the shale in heaving-shale formation isgenerally bentonltic in character and that upon being dispersed in watercarries a negative charge. It has now been found that if the colloidallydispersed particles, generally clay, in

drilling muds are positively instead of negatively charged, the swellingof heaving-shale can be prevented or lessened to a great extent.

In the preparation of drilling mud it is generally desirable to use afinely divided solid which will have a high colloidal dispersion inwater so as to produce a viscous, relatively stable mud with a minimumamount of solids. Bentonite has the aforesaid property and has beenfound to be a particularly satisfactory clay for use in drilling mud.Like other similar clays, bentonite carries a negative electrical chargewhen colloidally dispersed in an aqueous medium.

It has been found that such negatively charged colloids may be changedto positive colloids by the addition of one or more suitable watersoluble chemical compounds from the group: salts of metals wherein thepositive valence is three or more, such as thorium, aluminum, cerium andlanthanum salts; acid proteins such as acid gelatin or casein; basicdyes such as methylene blue, methylene green, methylene grey, methylviolet, Bismarck Brown R, Rhodamine B, acrifiavine, chrysoidin Y andchrysoidin R. By the addition of one or more of the foregoing materials,the negatively charged colloidal clay or bentonite may be firstneutralized and flocculated and upon a further addition, the neutralizedclay may be deflecforth in Table I.

Table I Go. of 1 Settling in Effect on Mixture No. of Salt molar salt 24hrs. Consistency shale in Charge haemltite solution 1 14 days 1 99 25 298 22 5 95 .18 9O 12 Y 80 6 Slightly positive. 75 4 D0. 70 1 65 0. 5 2575 23 35 65 1O 50 50 8 60 3 Positive, 70 3O 4 8O 20 8 culated and remainin a stable dispersed state as positively charged particles; It is notdesirable to use the flocculated, neutralized particles in drilling mudsince these .particles are not stably dispersed, the particles readilysettling from an aqueous dispersion medium. When such a positivelycharged clay as, for example, bentonite, is dispersed in water and usedas drilling mud, the shale in heaving-shale formations does not swell orslough off into the hole Table II Mix- 00.0! Amount I Cc. of Amount ofture Dye Salt 1N salt Suspensord of sus Stability Charge No. 5% dyesolution pensoid H20 18 Methyl violet.-- 10 Th(NOz)4. 1.5 Bentonlte 5%sus- Mud dilut- Flocculate llin None.

pension). ed to 100 1 day.

cc. 20 0.0 .do 50 do Solidfioc Do. 15 Th(N0 3.0 .....do 50 .-d0 0.1KSlightly posiwe. 20 .do. 3.0 .-.do 50 .d0... O.K Positive. 20 do 1.5 do50 do O.K Do. 30 0.0 .do 50 do Flocculated... None. 30 Th(NO 2.5 ....do50 d0 O.K Positive. 10 d 2.5 ...do 50 .do 2c1cgts1ettledin None.

rs. 10 do 2.0 50 .do 9cc.settledin Do. 18 hrs. 31 do v 30 do 2.0 do ..doO.K Positive.

and the bentonite particles remain stably dispersed. The ability of thepositively charged bentonite to prevent'swelling of the shale isbelieved to be due to neutralization of the negative charges on theshale particles in the subsurface formation by the positive charges onthe bentonite in the drilling mud with resultant formation of aflocculated film of shale and bentonite on the exposed surface of theshale formation in the bore hole. The flocculated materi'a'l forms anextremely coherent layer and adheres tightly to the surface of theformation, thus substantially preventing further neutralization ofcharges between the clay of the shale v the ingress of further water tothe formation,

Mixture No. 28, which contained no thorium nitrate gave no charge on thecataphoresis test and'produced solid flocculation when permitted tostand. Mixture No. 19, which contained the same amount of dye as mixtureNo. 28 and in addition 1.5 cc. of thorium nitrate had a positive chargeand the stability was satisfactory. No flocculation occurred in thismixture upon standing for one day. The same is true of mixture No. 27,which contained 3 cc. of thorium nitrate.

Mixture No. 26 was also satisfactory, although what unstable, asdemonstrated by mixtures Nos.

29 and 32.

When two materials of opposite electrical charge react, the amount ofeach material which is afiected is inversely proportional to theproportion of replaceable base which is present in a given weight of theparticular material. In view of the variations in the amount ofreplaceable base in the various dispersed particles such as bentoniticclays, and in the varying degree of effectiveness with which the varioussalts impart positive charges to colloidally dispersed particles, it isapparent that the relative quantities of clay or other material to besuspended and salt may vary over a rather wide range. The amount of saltrequired may be readily determined by a cataphoresis test using atBurton apparatus or other similar testing device. An amount of additive,somewhat in excess of that amount required to impart a positive chargeto the dispersed particles, is preferably used. In general. the amountsof the salts which are used fall between the ranges oi 1 part of salt to5 parts oi of dry bentonite or other material, to 3 parts of salt -to 1part of dry bentonite or other material to be suspended. While the saltmaybe mixed with the material to be suspended in the dry state and themixture subsequently dispersed in water as required, it is preferred toadd the salt dissolved in water to mud in which the bentonite or othermaterial to be suspended is already dispersed.

The term bentonite as used herein is used in a generic sense asincluding all clays having highly colloidal characteristics whether ornot they are true bentonite.- The salts which are useful are thosepolyvalent metal salts having a valence of three or more and aresufficiently soluble in water to impart the desired positive charge tothe suspended material.

Instead of using a polyvalent salt alone to obtain the desired charge, acombination of salt and basic dye or acid protein may be usedto obtainthe desired charge.

While an effort has been made to explain the theory by which positivelycharged colloidally dispersed particles in drilling mud provide drillingmud which prevents the heaving of heavingshale formations, it will beunderstood that the invention is not to be limited by any particulartheory of operation.

It is claimed:

1. In the drilling of earth bores the step of circulating through thebore during the drilling operation a mud containing positively chargedsuspended mineral particles to which the positive charge has beenimparted by soluble salts of metals, selected from the group consistingof aluminum, thorium. cerium and lanthanum.

2. In the drilling of earth bores, the step of circulating through thebore during the drilling operation mud containing normally negativelycharged colloidally dispersed mineral particles and suflicient solublesalts of metals, selected from the group consisting of aluminum,thorium, cerium and lanthanum to impart a positive charge to saidmineral particles.

3. In the drilling of earth bores, the step of circulating through thebore during the drilling operation a mud containing suspended bentoniteand weighting material and sufllcient soluble salts of metals, selectedfrom the group consisting of aluminum, thorium, cerium and lanthanum toimpart a positive charge to the bentonite.

4. A drilling mud comprising an aqueous suspension of normallynegatively charged'solid particles and sufiicient soluble salts ofmetals, from the group consisting of aluminum, thorium, cerium andlanthanum to impart a positive charge to said particles.

5. A drilling mud comprising an aqueous suspension of bentonite andsufllcient soluble salts of metals. selected from the group consistingof aluminum, thorium, cerium and lanthanum to impart to the bentonite apositive charge.

6. A drillingmud in accordancewith claim 5 containing barite. r

7. A drilling mud comprising an aqueous 'suspension of positivelycharged solid particles of colloidal size to which the positiye chargehas been imparted by soluble salts of "metals, selected from the groupconsisting of aluminum, thorium, cerium and lanthanum.

'8. A composition useful in the preparation of drilling muds comprisinga mixture of bentonite and soluble salts of metals selected from thegroup consisting of aluminum, thorium, cerium and lanthanum, the solublesalts of metals being present in amount sufllcient to impart to thebentonite particles a positive charge when suspended in water.

9. A composition useful in the preparation of drilling mud comprisingcomminuted solid mineral particles having a negative charge whensuspended in water and sufilcient salts of metals selected from thegroup consisting of aluminum, thorium, cerium and lanthanum to impart apositive charge to said particles when suspended in water.

10. In the drilling of earth bores the step of circulating through thebore during the drilling operation mud containing positive chargedsuspended mineral particles to which the positive charge has beenimparted by the combination of a basic dye and a salt of a metalselected from the group consisting of aluminum, thorium, cerium andlanthanum, the dye or the salt alone being insurficient to impart thepositive charge.

11. The step in accordance with claim 10 in which the dye is methyleneblue.

12. The step in accordance with claim 10 in which the salt is thoriumnitrate.

13. The step in accordance with claim 10 in which the dye is methyleneblue and the salt is thorium nitrate.

14. A composition useful in the preparation of drilling mud comprisingbentonite, basic dye and a salt of a metal selected from the groupconsisting of aluminum, thorium, cerium and lanthanum, the amount ofbasic dye and salt being sufiicient to impart a positive charge to thebentonite when suspended in an aqueous medium, the dye or the salt alonebeing insufficient to impart the positive charge.

15. A composition in accordance with claim 14 in which the salt isthorium nitrate.

16. A composition in accordance with claim 14 in which the salt isthorium nitrate, and the dye is methylene blue.

1'7. The step in accordance with claim 1 in which the salt is a thoriumsalt.

18. The step in accordance with claim 1 in which the salt is thoriumnitrate.

DONALD C. BOND.

